gh-96488: Fix build failure with older versions of GCC

[chrismile]

This PR fixes #96488, microsoft/vcpkg#26573, rbgirshick/py-faster-rcnn#706, LSSTDESC/CCL#270. These issues happended when runtime_library_dirs was used with distutils on systems with older versions of GCC not supporting the -R flag.

In rbgirshick/py-faster-rcnn#706, it was proposed to fix the problem by replacing the string "-R" in https://github.com/python/cpython/blob/main/Lib/distutils/unixccompiler.py#L261 by "-Wl,-R". However, the problem comes not from the fact that this line is wrong, but from _is_gcc(compiler) not accepting the compiler name cc as a possibly valid alias for GCC. On Linux, cc is a symlink to the default C++ compiler. In this PR, cc is now resolved to the actually used compiler. Thus, _is_gcc works correctly now for the compiler alias cc, and using runtime_library_dirs no longer results in compiler errors on older versions of GCC.

• Issue: Build failure with GCC <= 9.4 when using runtime_library_dirs #96488

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[ghost]

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[chrismile]

It seems to me that the build failures for Tests / Windows (x64) and macOS are unrelated to this PR. Please correct me if I'm wrong.

[hauntsaninja]

Closing as per #96487 (comment)